Late-night host Jimmy Fallon posed a tough question to GOP presidential nominee Donald TrumpDonald TrumpFormer defense secretary Esper sues Pentagon in memoir dispute Biden celebrates start of Hanukkah Fauci says lies, threats are 'noise' MORE in his Thursday appearance on "The Tonight Show:" "Can I mess your hair up?"

Fallon told Trump he wanted to do something "not presidential," since Trump could be president-elect in a few weeks. 

"I'm not liking the sound of this," Trump joked.

Fallon then asked if he could mess up Trump's famous hair. Trump cringed but relented, and quipped that he hoped people at a rally later that day in New Hampshire would understand.